GALEX file naming conventions

GALEX file names contain a prefix, a suffix and an extension (e.g. AISCHV2_153_29114_0002_sv11-xd-mcat.fits,

or

MISDR1_29079_0383_002-xd-int.fits).

The prefix contains alphanumeric characters of unspecified length, but contains no hyphens or periods (e.g. AISCHV2_153_29114_0002_sv11 and "MISDR1_29079_0383_002" above). The first 3 characters of the prefix generally map to the survey. Filenames for all-sky survey

(AIS) data will have _sv## at the end of the prefix, where the ## gives the number of the sub-visit.

The filename suffix contains delimited file type descriptor strings (e.g. "-xd-" in both cases above). The filename suffix may begin with a band (FUV/NUV) or mode (direct/imaging/opaque) substring:

• -nd- NUV direct (imaging)
• -fd- FUV direct (imaging)
• -xd- Band-merged direct (imaging)
• -ng- NUV grism
• -fg- FUV grism
• -xg- Band-merged grism
• -no- NUV opaque
• -fo- FUV opaque

Note that the file name is preceded by a period. Unless otherwise indicated, files transmitted to MAST are FITS binary files adhering to contemporary usage standards defined in http://archive.stsci.edu/fits/fits_standard/. The responsibility for verification of mission files transmitted in this format rests with the GALEX SOC. The file extension names are listed as follows:

.fits

Any FITS formatted file.

.txt

An ascii text file.

Filename extensions - pipeline files

Filename extensions are preceded by a period. Unless otherwise indicated, files transmitted to MAST are FITS binary files adhering to contemporary usage standards defined in http://archive.stsci.edu/fits/fits_standard/. The responsibility for verification of mission files transmitted in this format rests with the GALEX SOC. The file extension names are listed as follows:

.fits

Any FITS formatted file.

.txt

An ascii text file.

 

  

Note addition of * and .fits in the extension names below. The pend_obs file is an addition.

* acs.fits

Attitude control command file (for each eclipse).

* ins.fits

Instrument settings file (for each eclipse).

etf.fits

Eclipse time file.

obs.fits

Observe file

* pdb.fits

Plan data base. Contains list of plans.

* tdb.fits

Target data base. Contains list of targets.

* pend_obs.fits

Observations pending. Contains observation list.

  

These files contain binary FITS tables which will not be stored in the Data Base but along with calibration files are not ordinarily used or accessible by users through it. Database metadata and Table entries may be extracted from FITS headers if necessary.

-scst.fits

Aspect solution and state record file. Will be generated from hkfile and hksc and modified by RTA.

-raw6

Raw time-tagged photon data Single visit, single tile raw6 photon records. Time-tagged binary FITS table of photon records. May be broken down into segments

	T       time in seconds
	Byte1   8-bits of photon X, Y, Q, XA data
	Byte2   8-bits of photon X, Y, Q, XA data
	Byte3   8-bits of photon X, Y, Q, XA data
	Byte4   8-bits of photon X, Y, Q, XA data
	Byte5   8-bits of photon X, Y, Q, XA data
	Byte6   8-bit time offset from photon header time
	flags

-x

Extended photon record. Processed, time-tagged photon data

Primary image null. Binary FITS table (extension 1) with 11 fields per row.

 T	Time
 x, y	detector position
 X,Y,Z	J2000 position of photon in X,Y,Z coordinates (unit sphere)
 val	photon XA value
 q	photon pulse height
 flags	photon flag
 Thetax, Thetay	Position of photon in focal plane

Target level - image files

These files contain binary FITS images which are not to be stored in the database, but which the archive user will be able to download upon command. Database metadata and table entries will be extracted from FITS headers.

Postage stamp binaries may be generated and stored in database from some of the images described below.

-(n or f)d-cnt

Total count map (J2000) cnts pixel

FITS 2-D image. Dimensions are RA--TAN, DEC-TAN. Header uses FITS WCS standard. Units are in counts.

-(n-f)d-rr

is sensitivity times exposure time (i.e. seconds/pixel)

FITS 2-D image. Dimensions are RA--TAN, DEC-TAN. Header uses FITS WCS standard. Units are in cm s Å .

-(n or f)d-int

is Photons (counts) per pixel per second corrected for the relative response. Note that "-int.fits" is equal to "-cnt.fits" divided by "-rrhr.fits".

FITS 2-D image. Dimensions are RA--TAN, DEC-TAN. Header uses FITS WCS standard. Units are in cnts pixel cm s Å

-(n or f)d-exp

is an image of the time (in seconds) spent observing within the GALEX field of view (no response correction). When computing magnitudes (consistent with our -mcat catalog) use the formula: MAG = -2.5 * log_10( FLUX ) + ZPMAG
where FLUX is in counts per second (from the -int image), and where ZPMAG = 20.08 (NUV) and 18.82 (FUV).

FITS 2-D image. Dimensions are RA--TAN, DEC-TAN. Header uses FITS WCS standard. Units are in cnts/ pixel cm s Å

-(n or f)d-wt

Weight map/Mask for source extraction

FITS 2-D image. Dimensions are RA--TAN, DEC-TAN. Header uses FITS WCS standard. Units are in cnts/ pixel cm s Å

-(n or f)d-cat

Extracted source catalog from single band

Primary image null. Binary FITS table (extension 1) with 49 fields per row. Fields follow standard (or modified) Sextractor outputs: Isophotal (standard and corrected), aperture, Kron, ``Best'' magnitudes and errors, Background, detection threshold, centroid position (image, world coordinates), peak position, shape parameters (semi-major, minor axes, theta angle, ellipticity, elongation, moments, fwhm), extraction flags and crude star-galaxy separation.

-(n or f)d-dose

Dosage map (total counts in detector coordinates)

FITS 2-D image. Dimensions are x, y in detector coordinates. Units are in counts.

Target level - merged catalog

These files contain binary FITS tables which contain data that will be stored directly in database. Database metadata and table entries may also be extracted from FITS headers.

-xd-mcat

Merged source catalog (both bands)

Primary image null. Binary FITS table (extension 1). Fields are: ObjectID, band merger outputs (combined ra, dec, match probability, separation, ambiguity, match flags) and combined catalogs from each band. As with the -cat file, fields for each band conform to standard (or modified) Sextractor outputs: Isophotal (standard and corrected), aperture, Kron, ``Best'' magnitudes and errors, Background, detection threshold, centroid position (image, world coordinates), peak position, shape parameters (semi-major, minor axes, theta angle, ellipticity, elongation, moments, fwhm), extraction flags and crude star-galaxy separation.

Target level: grism-specific files

• pri             (Not available in the ERO.)

  This file contains the image strips for individual exposures for each spectral-extracted source. The photon data, response, and masking images are recorded for each source. Masking for the image strip is stored in the response image (neighbor masking) and the photon data image (other masking) as negative numbers. Spectral response variations with position (column) are stored in the response image in the final row. These images contain the total accumulated photon data for each source for a given single visit or exposure. Each source has its own FITS header unit. The order of the image strips is identical to the order of sources in the extracted source catalog given in the (root)-gsax.fits file.

  First Header Unit: Grism angle used for these extractions, total exposure time, total number of spectrally extracted sources (ECOUNT), field center, and other extraction parameters.

  Second through ``N" Header Unit: Accumulated image strips for photon data and response for any of N-1 sources in the field of view. The header portion defines the image dimensions (PRI_NC,PRI_NR). The scale is given in arcseconds per pixel in both spatial and dispersion directions. The header key words also include the blue limit offset in arcseconds (ARCSEC1) relative to the object center (undeviated) position, which is used to derive the wavelength scale. The image strips typically cover multiple grism orders, e.g. 1st, 2nd, and 0th. The image data is stored as 2-byte integers, which can be scaled to true data values using the header key words DATZERO, DATSCALE, RSPZERO, and RSPSCALE.

• prc

  This file contains the stacked or summed image strips for multiple exposures for each spectral-extracted source. The format is the same as for the pri files, except that masking has been applied before summing. That is, all masked pixels in the individual (pri) image strips were set to zero before summing.

  First Header Unit: Contains the filenames of all *-pri.fits which have been stacked, as well as their respective grism angles.

  Second through ``N" Header Unit: Accumulated image strips for photon data and response for any of N-1 sources in the field of view.

• prm

  This file contains the medianed image strips for multiple exposures for each spectral-extracted source. The format is the same as for the pri files, except that masked pixels have been ignored by the median value calculation.

  First Header Unit: Contains the filenames of all *-pri.fits which have been medianed, as well as their respective grism angles.

  Second through ``N" Header Unit: Accumulated image strips for photon data and response for any of N-1 sources in the field of view.

• gsax

  General information (binary FITS table). This file contains parameter information, as well as a source list table including extraction parameters for each source. This source list catalog is created on the first exposure and read in and used for each subsequent exposure. This file also contains a table of data for each accumulated exposure.

  First Header Unit: Header key words contain various extraction parameters for ``galaxspac" (spectral accumulation program). These include the flux cutoff (i.e., the brightest ``N" sources) used on the direct image source catalog, the field RA,Dec origin, the masking parameters, band number, the total number of exposures (or orbits) and exposure time accumulated.

  Second Header Unit: Extracted source list. This contains a source catalog of all the sources which have been extracted. This includes the RA,Dec positions, global IDs, direct image FUV and NUV flux rates, direct image FWHMs, and extraction parameters (object and background widths and length of the spectrum) for each source.

  Third Header Unit: Accumulated exposures (orbits) list. This contains a catalog of all the photon data sets added into the image strips. This includes all the *-pri.fits filenames, grism angles, field offsets used (x, y, twist (rotation) relative to the direct image source positions), exposure times, and reduction dates.

• xsp

  An xsp file, labeled *-fg-xsp and *-ng-xsp, is extracted for each wavelength band. Each file represents two sequential spectral orders as recorded along the spectral axis on the detector, so units are photons per second per arcsecond. Each source has its own FITS header unit, in the same order as the data occur in the -pri.fits file.

  First Header Unit: Contains the header key word for the total number of sources extracted (ECOUNT).

  Second through ``N" Header Unit: Spectra for each source and its computed 1 sigma error. Spectra are given in photons/second/pixel vs. offset arcsecond (position relative to object center or undeviated object position).

• gsp

  There are three gsp files for each spectrum: *-fg-gsp, *-ng-gsp, and *-xg-gsp. The first two are grism-order merged ( =1 and 2 for NUV, and 2 and 3 for FUV), flux calibrated, and rebinned onto a linear wavelength scale. The third is the conjoined spectrum of the first two. The units for these are photons/second/cm/Angstrom. The fg-gsp and ng-gsp files are for many purposes rendered obsolete by the xg-gsp file. Since the dispersion is linear, the zero point and dispersion of the wavelength scale are given as table entries. Two of the vector entries (flux and error) are for a simple (summation) extraction, and two vectors are for the optimal extraction.

  Each file consists of a short primary header (giving the number of spectra in the file) and a single extension. In this extension each row gives spectral information (default fluxes, associated errors, optimally extracted fluxes, associated errors) for an astronomical object. These rows are listed in order of their appearance in the extracted source catalog in the (root)-gsax.fits file. However, ``masked" sources appearing in the gsax file are not extracted as spectra and thus not included in the gsp file listing.

  

  

 
 Flag name   |   Bit   | Flag_N value |   Meaning                                 | Notes
             | (LSB=1) |  (base 10)   |                                           |
 ------------|---------|----------------------------------------------------------|--------
 Edge        |    1    |   1          | Detector bevel edge reflection (NUV only) | 1,2
 ------------|---------|----------------------------------------------------------|--------
 Window      |    2    |   2          | Detector window reflection (NUV only)     | 1,2
 ------------|---------|----------------------------------------------------------|--------
 Dichroic    |    3    |   4          | Dichroic reflection                       | 1,2
 ------------|---------|----------------------------------------------------------|--------
 Varpix      |    4    |   8          | Varible pixel based on time slices.       |
 ------------|---------|----------------------------------------------------------|--------
 Brtedge     |    5    |  16          | Bright star near edge of field (NUV only).|
             |         |              | Just like #1 but with a higher count rate | 
             |         |              | requirement (about 10 cps) on the         | 
             |         |              | generating star. Cuts down on false       | 
             |         |              | positives at the cost of a higher false   | 
             |         |              | negative rate.                            | 
 ------------|---------|----------------------------------------------------------|--------
 Rim         |    6    |  32          | Detector rim (annulus) proximity          | 3
             |         |              | (>0.6 deg from FOV center).               | 
 ------------|---------|----------------------------------------------------------|--------
 Dimask      |    7    |  64          | Dichroic reflection artifact mask flag.   |
             |         |              | Used only when a coadd has enough visits  | 
             |         |              | at enough position angles that masking    | 
             |         |              | the dichroic reflection doesn't decrease  | 
             |         |              | flux by more than 1/3.                    | 
 ------------|---------|----------------------------------------------------------|--------
 Varmask     |    8    | 128          | Masked pixel determined by varpix.        |
 ------------|---------|----------------------------------------------------------|--------
 Hotmask     |    9    | 256          | Masked detector hotspots.                 |

 

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